The present invention relates to the enclosing and sealing of elongate substrates, for example electrical or telecommunications cables, and especially joints between such cables.
WO 91/00601 (Raychem) discloses a joint closure for an electrical cable. The closure comprises a heat-recoverable fabric sleeve wrapped around a sealing mastic, the ends of the sleeve being secured with a closure member. Two scaling materials may be used in such a closure, one material acting as a blocking material having both a higher viscosity at room temperature and a melt viscosity which is higher than the viscosity of the other material.
According to a first aspect, the invention provides an article for enclosing an elongate substrate, the article comprising a container at least in use, a first sealing material and a second scaling material, such that the first scaling material is located between the second sealing material and an end of the container, characterised in that both sealing materials are polymeric and in that the first sealing material has a higher softening point and a higher melt viscosity at a defined temperature than the second sealing material.
According to a first aspect, the invention provides an article for enclosing an elongate substrate, the article comprising a container containing, at least in use, a first sealing material and a second scaling material, such that the first sealing material is located between the second sealing material and an end of the container, characterised in that both sealing materials are polymeric and in that the first sealing material has a higher softening point and a higher melt viscosity at a defined temperature than the second sealing material.
According to a second aspect, the invention provides a method of enclosing an elongate substrate, the method comprising the steps of:
a) placing first and second sealing material on the substrate; and
b) placing a container around the first and second scaling material and around the substrate, such that the first sealing material is located between the second polymeric sealing material and an end of the container;
which method is characterised in that both sealing materials are polymeric and in that the first sealing material has a higher softening point and a higher melt viscosity at a defined temperature than the second sealing material.
Preferably, there are at least two portions of the first polymeric sealing material. At least in use, at least one portion of the first polymeric sealing material is preferably placed on each opposite side of the second polymeric scaling material, on the elongate substrate.
According to a third aspect, the invention provides an article for enclosing an elongate substrate, comprising:
(a) a container; and
(b) a polymeric sealing material;
at least in use, the polymeric sealing material being located within the container.
According to a fourth aspect, the invention provides a method of enclosing an elongate substrate, comprising:
(a) placing a polymeric sealing material on the substrate; and
(b) placing a container around the polymeric sealing material and the substrate.
In use, the polymeric sealing material is preferably heated, preferably to above 100xc2x0 C., to cause it to melt and to flow, and to conform closely to the substrate.
In some embodiments, the polymeric sealing material may be curable. In such embodiments, the invention preferably further comprises a curing agent for curing the polymeric sealing material. The curing agent may be part of the polymeric sealing material, or intimately mixed with the sealing material, or it may be separate from the sealing material. The curing agent may, for example, be present in the form of pellets, contained in microcapsules, provided as a layer on the sealing material or be provided in or on another component, e.g. a sheet, a bag, or a mesh. If the curing agent is not provided as part of, or intimately mixed with, the sealing material, it preferably becomes mixed with the sealing material during heating.
The polymeric sealing material may be separate from the container, e.g. in the form of a layer. The sealing material, or at least a portion of it, may however be provided on an inner surface of the container, e.g. as a layer. In this case, steps (a) and (b) of the methods according to the invention may be one and the same step, i.e. placing on the substrate a container which has polymeric sealing material (e.g. a layer of polymeric sealing material) on an inner surface thereof.
For the avoidance of doubt, it should be understood that any or all features of each aspect of the invention may be combined with any or all features of any or all other aspects of the invention.
The container is preferably dimensionally-recoverable, e.g. dimensionally-shrinkable. It is especially preferred for the container to be dimensionally heat-recoverable. The container may, for example, be in the form of a tube or a sleeve. It may be in the form of a sheet or the like which may be wrapped around the elongate substrate, e.g. it may be a so-called wraparound sleeve. The wraparound sleeve preferably has closure rails along opposite longitudinal edges, and a separate channel component by means of which the wrapped sleeve is retained in a closed configuration during use.
Once the container has been placed (e.g. wrapped) around the elongate substrate, it is preferably then heated (e.g. by means of a torch flame or by hot air) in order to cause it to recover around the substrate. This heating preferably causes the or each polymeric sealing material to melt and to flow, and to conform closely to the substrate. Once the container has been recovered, the polymeric sealing material preferably substantially fills the volume between the container and the substrate, leaving substantially no gaps.
According to the first and second aspects of the invention, there is a first polymeric sealing material which has a relatively high softening point and/or a relatively high melt viscosity at a defined temperature, and there is a second polymeric sealing material which has a relatively low softening point and/or a relatively low melt viscosity at said defined temperature. (These physical characteristics of each material are xe2x80x9chighxe2x80x9d or xe2x80x9clowxe2x80x9d relative to the corresponding values of the other material.) The softening point of the first polymeric sealing material is preferably at least 80xc2x0 C., more preferably at least 85xc2x0 C., e.g. at least 88xc2x0 C. The softening point of the second polymeric sealing material is preferably lower than 80xc2x0 C., more preferably lower than 78xc2x0 C., e.g. lower than 76xc2x0 C. The relative melt viscosity of each sealing material is preferably as measured at 100xc2x0 C., and at this temperature the melt viscosity of the first polymeric sealing material is preferably at least 100 Pas (Pascal seconds), more preferably at least 150 Pas. At the same temperature, the viscosity of the second polymeric sealing material is preferably lower than 60 Pas, more preferably lower than 50 Pas.
The softening points of the sealing materials are preferably as measured in accordance with ASTM standard test method E28-97 (xe2x80x9cSoftening Point of Resins by Ring-and-Ball Apparatusxe2x80x9d). The melt viscosities of the sealing materials are preferably as measured in accordance with ASTM standard test method D-3236-88, using a Brookfield model HBT viscometer, and spindle SC-27.
The use of two polymeric sealing materials with different softening points and/or different melt viscosities has the advantage that two conflicting requirements can be met, namely that the sealing material should flow and conform closely to the substrate during the heating operation, but that it should not escape from the container before it has solidified. The first polymeric sealing material preferably acts as a dam to prevent the more fluid molten second polymeric sealing material from flowing out of the container. Preferably each longitudinal end of the container (e.g. sleeve) has a quantity of the first sealing material to block the escape of the more centrally located second sealing material.
The polymeric sealing material may be provided in the form of blocks, sheets, or the like. Alternatively it may be in the form of pellets or in some other particulate or loose form. The sealing material may be contained in or retained by a delivery system, e.g. such as one or more bags, pouches, meshes or the like. It is particularly preferred for the sealing material to be supplied in the form of pellets contained in one or more mesh bags or pouches. If more than one bag or pouch is used, they may be separate or joined together. When the sealing material is melted, it preferably flows through the mesh and into intimate contact with the substrate. The mesh is preferably formed from a polymeric material, which preferably has been cross-linked so that it does not melt when the sealing material is heated.
The polymeric sealing material preferably comprises polyamide. Preferred polyamides are based on dimerised fatty acids and/or aliphatic amines. If a curing agent is used, this is preferably an epoxy material. However, other curing agents may be used, e.g. peroxides or acrylate terminated prepolymers (e.g. such as polyurethanes or polyesters etc). The sealing material may, for example, be acid terminated or amine terminated. If the sealing material is amine terminated it will normally react quickly with an epoxy curing agent, and therefore the curing agent is preferably kept separate from the sealing material until the sealing material needs to be cured.
Other polymeric sealing materials may be used, for example: polyethylene waxes; functionalized polyethylene waxes; polyethylene copolymers (e.g. ethylene vinyl acetates and/or ethylene butyl acetates); polyurethanes.
As already mentioned, the polymeric sealing material may be supplied as a layer, more preferably on an inner surface of the container. The layer of sealing material may be continuous, but preferably it is discontinuous. The layer preferably includes a plurality of discontinuities, e.g. gaps, holes, indentations, recesses, protrusions or the like. For example, the layer may comprise a series of strips or blocks, e.g. separated by gaps. Additionally or alternatively it may comprise a series of alternating protrusions and recesses, e.g. ridges and valleys. The layer may comprise an array of holes, gaps or recesses, and/or protrusions or the like.
The inventors have found that there are two main advantages to the layer of sealing material being discontinuous. Firstly, it may assist the placing of the container around the substrate, particularly when the container is in the form of a wraparound sleeve (e.g. the discontinuities in the layer may enable the container to retain its flexibility when this is desired). Secondly, it may enhance the ability of the sealing material to melt, flow, and conform around the substrate. This may, at least in part, be due to an increase in the surface area of the sealing material which the discontinuities may provide, and/or it maybe due to the shape or arrangement of the sealing material facilitating the speed of its melting and its ability to flow adequately.
The sealing material may be shaped in any of a variety of ways. It may, for example be extruded or moulded. Another possible method is to coat the sealing material onto the container, e.g. by pouring, injecting or spraying the sealing material onto the container. If the sealing material is shaped before it is applied to the container, it is preferably subsequently bonded to the container, e.g. by heat bonding.
If the sealing material is in the form of a layer, its thickness (prior to being melted and conforming around the substrate) is preferably no greater than 4.0 cm, more preferably no greater than 3.0 cm, especially no greater than 2.0 cm. The thickness of the layer is preferably at least 0.5 cm, more preferably at least 0.7 cm, especially at least 1.0 cm. The precise thickness of the layer, and if there is more than one layer, the number of layers, will be determined by the skilled person according to the particular requirements, especially the size and shape of the substrate, and the volume to be filled.
The invention is preferably used for enclosing and sealing a cable, e.g. an electrical cable or a telecommunications cable. More preferably, it is used for enclosing and sealing a joint or splice between two or more such cables. The invention is particularly suitable for enclosing a low voltage electrical power cable joint, especially a so-called branch-off joint. The joint may comprise a plurality of connections, or a single connector block, for example. Preferably the joint is substantially entirely encapsulated in the polymeric sealing material, preferably with substantially no voids or gaps. If a dimensionally-recoverable container (e.g. a heat-shrinkable sleeve) is used, the recovery of the container will normally drive the polymeric sealing material into any gaps, and cause it to conform closely to the substrate such that it is completely encapsulated in the sealing material. Another important advantage in using a heat-shrinkable sleeve is that after the sleeve has been heated (and shrunk) and is cooling down, re-crystallization of the sleeve material normally occurs, which generally causes extra shrinkage of the sleeve. The temperature range in which this normally occurs is about 85-100xc2x0 C., at which temperatures at least some, and normally substantially all, of the polymeric sealing material will generally still be molten (since the re-crystallization or hardening temperature is often lower than the softening temperature). This means that as the sleeve cools down and the polymeric sealing material begins to harden (but before most of it has hardened) the sleeve continues to drive the sealing material into any gaps or voids in and around the substrate. This generally ensures a void-free encapsulation of the substrate. In embodiments of the invention which are electrical power cable joint closures, the closure preferably meets the Cenelec load-cycling specification HD623 for xe2x80x9cJoints, stop ends and outdoor terminations for distribution cables of rated voltage 0.6/1 Kvxe2x80x9d. This specification defines a standard procedure for testing the sealing and insulation reliability of low voltage joint closures and terminations. The test comprises a series of xe2x80x9cload cyclesxe2x80x9d in which the electrical cables of the joint have electrical current passed through them in order to raise the temperature of the conductors to between 5 and 10xc2x0 C. above the maximum rated temperature of the cables. (The maximum rated temperature of PVC insulated cables is 70xc2x0 C., and for polyethylene insulated cables it is 90xc2x0 C.) Each cycle comprises a two hour period during which this elevated temperature is maintained, after which the electrical current is switched off and the conductors are allowed to cool to within 10xc2x0 C. of the ambient temperature within a period of not less than three hours. The entire test comprises 63 such load cycles with the joint closure in air, followed by 63 load cycles with the joint closure immersed in water (with a water head of 1 m). In order to pass the test, after the load cycling the electrical conductors must withstand a specified a.c. test voltage, and the insulation resistance (according to a specified test) must be at least 50 Mxcexa9. This Cenelec specification is a rigorous test, and the present inventors have found that by making a joint closure in accordance with the invention, the requirements of the specification may normally be achieved. In particular, by using the first and second polymeric sealing materials (as defined herein) it has been found that the stringent load cycling test for polyethylene insulated cables can normally be passed.